Question -
Answer -
Estimation of halogens
Halogens are estimatedby the Carius method. In this method, a known quantity of organic compound isheated with fuming nitric acid in the presence of silver nitrate, contained ina hard glass tube called the Carius tube, taken in a furnace. Carbon andhydrogen that are present in the compound are oxidized to form CO2 andH2O respectively and the halogen present in the compound isconverted to the form of AgX. This AgX is then filtered, washed, dried, andweighed.
Let the mass of organiccompound be m g.
Mass of AgX formed= m1 g
1 mol of Agx contains 1mol of X.
Therefore,
Mass of halogen in m1 g of AgX 
Estimation of Sulphur
In this method, a knownquantity of organic compound is heated with either fuming nitric acid or sodiumperoxide in a hard glass tube called the Carius tube. Sulphur, present in thecompound, is oxidized to form sulphuric acid. On addition of excess of bariumchloride to it, the precipitation of barium sulphate takes place. This precipitateis then filtered, washed, dried, and weighed.
Let the mass of organiccompound be m g.
Mass of BaSO4 formed= m1 g
1 mol of BaSO4 =233 g BaSO4 = 32 g of Sulphur
Therefore, m1 gof BaSO4 contains 
Estimation of phosphorus
In this method, a knownquantity of organic compound is heated with fuming nitric acid. Phosphorus,present in the compound, is oxidized to form phosphoric acid. By adding ammoniaand ammonium molybdate to the solution, phosphorus can be precipitated asammonium phosphomolybdate.
Phosphorus can also beestimated by precipitating it as MgNH4PO4 by addingmagnesia mixture, which on ignition yields Mg2P2O7.
Let the mass of organiccompound be m g.
Mass of ammoniumphosphomolybdate formed = m1 g
Molar mass of ammoniumphosphomolybdate = 1877 g
If P is estimated as Mg2P2O7,
